Russian observers are putting the best face on the flurry of diplomatic activity, which also saw German Chancellor Angela Merkel jet into Moscow on Sunday to lay a wreath in honor of Russian Victory Day and hold talks with Mr. Putin. That, plus Mr. Kerry's visit, suggests that Western governments may be trying to limit the damage from their boycott of Russia's massive V-Day military parade last weekend, and at least keep open the lines of communication with Russian leaders in dealing with major global problems such as Ukraine, Syria, and Iran.

"Perhaps they're trying to make some course corrections. What they have been doing until now [sanctions and tough rhetoric] hasn't had the desired effect on Russia, so they are changing tactics," he says.

Kerry emerged from his nearly day-long meetings with Putin and Foreign Minister Sergey Lavrov talking up the value of keeping channels open between Washington and Moscow. "There is no substitute for talking directly to key decision makers, particularly during a period that is as complex and fast-moving as this is," he said. He also laid a wreath at a Sochi memorial for Russian soldiers killed in World War II – a conciliatory gesture after the West's Victory Day boycott.

Experts say Russia and the West may be willing to accept a long-term impasse over Ukraine. The main purpose of Kerry's visit, they say, was to ensure continued Russian cooperation in other vital areas, particularly the looming deadline for a final agreement between Iran and the P5+1 (five permanent UN Security Council members plus Germany) to curb Iran's nuclear program.

"We are now coming into the last six weeks of those negotiations," Kerry said. "And we all understand that unity has been key to bringing us where we are today."

But some Russian analysts warn that Ukraine itself could yet derail wider cooperation between Moscow and Washington unless the flagging Minsk peace process is bolstered by fresh initiatives.

"Both sides realize that the Ukraine conflict has been costly, and brought no benefits to anybody," says Viktor Kremeniuk, deputy director of the official Institute for USA-Canada Studies in Moscow. He says that forces on the ground might resume open warfare, and thus scramble any progress that's been made under the Minsk deal.

"Hopefully, there is a new urgency in the air about this crisis. It's time to stop head-butting one another over Ukraine, and start coming to some serious decisions about the way forward."